Sensors for gases are becoming an integral part of our technology-dependent lives, such as in cars (performance and emissions control), buildings (air quality management), factories (process control and leak detection) and food processing and packaging (freshness and ripeness control).
Medical diagnostics is yet another emerging area that requires low-cost and accurate detection and quantification of gaseous analytes. The presence of various gases (e.g., acetone, ammonia) at certain concentrations in breath, for instance, is linked to certain health conditions such as diabetes and failure of the kidney and liver.
Rapid and low-cost development of sensors of gas remains a major challenge for several reasons: i) use of expensive and unscalable detection methods (i.e. infrared gas sensors), ii) use of complex fabrication procedures (i.e. vapor phase grown ceramic thin films), iii) dependence on high temperatures for detection (e.g. metal-oxide sensors), iv) offer low level of selectivity, v) use of rigid/non-flexible materials, and vi) require frequent calibration for accurate readings.
Previous examples of paper-based sensors of gases involve the integration of carbon nanotubes, quantum dots or other forms of nanostructures on paper. These examples use the nanostructures as the active sensing material and the paper itself is only a scaffold.
Breathing is one of the primary vital signs used to diagnose the health status of patients; it is related to many common disorders and diseases, ranging from pulmonary and cardiovascular diseases to sleep-related disorders. Current methods of monitoring breathing require cumbersome, inconvenient and often expensive devices; In prior methods, the breathing patterns are recorded via insertion of a nasal cannula into the patient's nose. The cannula is attached to a pressure sensor, which measures the breathing of the patient. When the patient breathes through the mouth, however, this method of detection fails to sense the changes in breathing giving rise to false diagnosis. To mitigate this issue, other health parameters such as chest motion and blood oxygen levels are tracked. This requirement sets practical limitations on the frequency and duration of measurements. To circumvent the complications of on-site clinical testing, at-home testing of sleep apnea is being developed. For example, a cell phone assisted take-home sleep test included an array of sensors that correlated the blood oxygen levels and heart rate with occurrence of reduced or paused air flow during sleep. Although the overall system was satisfactory, the device was bulky (required 2xAAA batteries) and consisted of expensive components, increasing the cost of ownership.
Sleep apnea is a disorder in which the flow of air into and out of the lungs is fully or partially obstructed for at least 10 seconds continuously. This paused or shallow breathing is linked to a variety of health problems, including but not limited to cardiovascular diseases, stroke, and diabetes.
Take-home sleep apnea tests are available, such as AccuSom by NovaSom and WatchPAT. Current methods of detection hinder proper diagnosis of this condition because of two reasons: i) diagnosis is primarily done in clinical settings which is time-consuming and difficult for most patients to participate in, and ii) current take-home tests are too expensive and cumbersome to operate for patients to adopt these technologies. An effective solution to take-home sleep apnea testing still does not exist.
The most common strategy for diagnosis is to perform a sleep study at a clinical site. These studies often require an overnight stay and supervision of specialized personnel. From the initial discussions with the physician to the diagnosis from a complete sleep study can take up to six weeks. The inconvenience of these studies is the primary reason preventing people who suspect having sleep apnea from getting diagnosed.